Network analysis of the northern Benguela ecosystem by means of NETWRK and ECOPATH

Two software packages are available to analyze ecosystems and to compute ecosystem variables: NETWRK 4.2a and ECOPATH 4.0. A how model of the northern Benguela ecosystem was used to compare the outputs from these two packages. The northern Benguela ecosystem is a sub-system of the Benguela upwelling ecosystem off the coast of Southern Africa. The food web used in this study consists of 24 compartments, of which 22 were living and two were non-living compartments. NETWRK is a DOS-based package constructed in 'FORTRAN' by R.E. Ulanowicz, University of Maryland, in the late 1980s (updated in 1999 - version 4.2a), while ECOPATH is a Windows-based package written in 'Visual Basic' that uses the same methodologies as NETWRK but whose algorithms have been programmed based on the original descriptions with some differences in interpretation. There are fundamental differences between the input methodologies of the two packages, which leads to differences in their output. NETWRK takes the respiration of primary producers into consideration, while ECOPATH does not. This leads to various discrepancies in the calculation of throughput and all the parameters related to it, such as the ascendency and development capacity. In most cases, the differences are small enough that the interpretation of the results would bring the modeler to the same qualitative conclusion using ECOPATH or NETWRK. However, the mixed trophic impacts, Lindeman spine, primary production required and Finn Cycling Index, are markedly different for the two models. It is concluded that consolidating these models would be of enormous value to ecosystem analysis. (C) 2000 Elsevier Science B.V. All rights reserved.